It is known in the art to prepare a tissue sample which is to be used for diagnostic evaluation by first fixating the tissue sample followed by dehydration and embedding of the tissue sample. The conventional methods for fixation and dehydration of tissue specimens, however, are time consuming and utilize potentially toxic substances which release or may release malodorous vapors.
One conventional fixation technique uses formalin or formalin derivatives. Formalin is an aqueous solution of formaldehyde which may contain methyl alcohol. This conventional fixation method requires 8 to 24 hours for completion of the fixation process.
Conventional dehydration techniques use ethanol, toluene, or other organic solvents which are flammable, volatile, and potentially toxic. Time requirements for the conventional dehydration techniques are between 8 hours and four days.
In the past, improvements to fixation techniques have been attempted by using heat in order to accelerate the fixation of a tissue specimen. However, past fixation techniques using heat have been detrimental to the tissue specimen due to overheating or burning of the tissue specimen resulting in the loss of the tissue sample.
Conventional embedding techniques use paraffin or plastic monomers which undergo polymerization induced by benzoyl peroxide and heat. Sections of tissue samples embedded in paraffin are of inferior quality compared to plastic embedded samples. However, most plastic embedded techniques are time consuming, i.e., between 36 to 58 hours are required for optimal plastic embedding.
Conventional methods for adhesion of plastic sections to glass slides use pressure application combined with moderate heat. This approach requires between 8 to 18 hours.
Conventional techniques for plastic embedding do not remove the plastic from the tissue section. The presence of the plastic in the tissue section affects the affinity of the histologic stains to the cells. Dissolving of plastic is rarely done and, if so, requires in the range of 1.45 hours per set of tissue sections.
Conventional methods for staining of histologic sections use immersion of slides into containers filled with the particular histologic stains. Differential exposures to different stains result in preferential identification of various tissue components by selective staining. Conventional staining techniques such as trichrome stains require up to 80 minutes for completion of selective sequential staining.